Image Scanning Apparatus

ABSTRACT

An image scanning apparatus has a scanner configured to read an original sheet on a line basis at a constant line cycle and generate analog image data for each pixel of the line, and output the analog image data for each pixel at a pixel cycle, a power source including a DC/DC converter configured to convert a first DC voltage to a second DC voltage by applying a switching control to the first DC voltage at a switching cycle, the second DC voltage being supplied to the scanner, a convertor configured to sample the analog image data at the pixel cycle to convert the analog image data to digital image data, a sampling setting unit configured to set the pixel cycle, and a controller configured to cause the sampling setting unit to set the pixel cycle to be an integer multiple of the switching cycle of the DC/DC convertor.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims priority under 35 U.S.C. §119 from JapanesePatent Application No. 2014-241003 filed on Nov. 28, 2014. The entiresubject matter of the application is incorporated herein by reference.

BACKGROUND

1. Technical Field

The present disclosures relate to an image scanning apparatus.

2. Related Art

Conventionally, it is known that image scanning apparatuses have afollowing problem. That is, due to fluctuation in an output voltage of apower supply which is applied to a scanning device of the scanningapparatus, noises may be included in a read signal generated by thescanning device. For example, a DC power supply noise component due to aripple voltage which is generated due to a ripple voltage in the powersupply of the scanning device may be superposed on the read signal.

SUMMARY

There is known a conventional scanning apparatus which is configured toextract a noise component superposed on the read signal, and removes thesame by subtracting the extracted noise component from the read signal.

In such a technique, however, if photoelectric conversion elementsinside the scanning device output an electrical signal as the readsignal upon starting outputting the electrical signal, the color of thelight source cannot be switched one having a different color until allthe read signal has been output. According to a recent configuration,analog memories corresponding to the respective photoelectric conversionelements are provided inside the scanning device. Then, immediatelyafter reading an image for one line, the electrical signal for one lineis stored in the analog memory, so that a light control to switch thelight sources can be performed.

Since the electric signal for a previous line is output from thescanning device having the built-in analog memory as the read signal,the noise component in the read signal and the noise component of thepower source are different by one line. Therefore, in the conventionalimage scanning apparatus as mentioned above, it is necessary to adjusttimings of the noise components of the read signal and the power sourcein order to remove the noise components from the read signal.

In consideration of the above, according to the present disclosures,there is provided an improved image scanning apparatus in which, even ifa noise component is generated in the power source of the scanningdevice, the noise component does not have any influence on the readsignal.

According to aspects of the disclosures, there is provided an imagescanning apparatus, which has a scanner configured to read an originalsheet on a line basis at a constant line cycle and generate analog imagedata for each pixel of the line, and output the analog image data foreach pixel at a pixel cycle, a power source including a DC/DC convertorwhich is configured to convert a first DC voltage to a second DC voltageby applying a switching control to the first DC voltage at a switchingcycle, the second DC voltage being supplied to the scanner, a convertorconfigured to sample the analog image data at the pixel cycle to convertthe analog image data to digital image data, a sampling setting unitconfigured to set the pixel cycle, and a controller configured to causethe sampling setting unit to set the pixel cycle such that the pixelcycle is an integer multiple of the switching cycle of the DC/DCconvertor.

Since the pixel cycle is set to the integer multiple of the switchingcycle, the pixel cycle synchronizes with the switching cycle.Accordingly, fluctuation of the voltage of the power source due to aswitching control is constant, and influence of the voltage fluctuationon the analog image data is removed or well suppressed.

BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS

FIG. 1 schematically shows an inner structure of an image scanningapparatus viewed from a front side according to an illustrativeembodiment of the disclosures.

FIG. 2 is an enlarged view of a scanner employed in the image scanningapparatus according to the illustrative embodiment of the disclosures.

FIG. 3 is a block diagram showing a power supply configuration of theimage scanning apparatus according to the illustrative embodiment of thedisclosures.

FIG. 4 is a block diagram showing an electrical configuration of theimage scanning apparatus according to the illustrative embodiment of thedisclosures.

FIG. 5A shows a relationship between a ripple voltage and an analogvoltage for an example 1, which is a comparative example.

FIG. 5B shows a relationship between the ripple voltage and the analogvoltage for an example 2 according to the illustrative embodiment.

FIG. 5C shows a relationship between the ripple voltage and the analogvoltage for an example 3 according to the illustrative embodiment.

FIG. 6 is a flowchart illustrating a maintenance main process accordingto the illustrative embodiment of the disclosures.

FIG. 7 is a flowchart illustrating a scanning main process according tothe illustrative embodiment of the disclosures.

FIG. 8 is a flowchart illustrating a line cycle determining processaccording to the illustrative embodiment of the disclosures.

DETAILED DESCRIPTION OF THE EMBODIMENT

Hereinafter, referring to the accompanying drawings, an image scanningapparatus 1 according to an illustrative embodiment of the disclosuresand its modifications will be described.

<Mechanical Configuration of Image Scanning Apparatus>

In FIG. 1, up, down, front and rear directions are indicated by arrows.The image scanning device 1 has a sheet feed tray 2, a main body 3, anda discharge tray 4. Further, the image scanning device 1 has anoperation panel 5 and a display 6, which are arranged on an uppersurface of the main body 3. The operation panel 5 is provided with apower switch and other setting buttons through which a user can inputoperational commands and the like. For example, the operation panel 5 isprovided with a selection button to select three-color mode (color mode)or single-color mode (mono mode), an operation button to set aresolution, and the like. The display 6 is provided with an LCD (liquidcrystal display) and displays operational statuses of the image scanningapparatus 1.

A sheet conveying passage 20 is defined inside the main body 3. Each oforiginal sheets GS placed on the sheet feed tray 2 is conveyed, alongthe sheet conveying passage D, in a conveying direction FD, anddischarged from the main body 3 onto the discharge tray 4. A sheet feedroller 21, a sheet separation pad 22, an upstream conveying roller pair23, a scanner 24, a platen glass 25, a downstream conveying roller pair26 are arranged along the sheet conveying passage 20.

The sheet feed roller 21 feeds, in association with the sheet separationpad 22, multiple original sheets GS placed on the sheet feed tray 2 oneby one. The upstream conveying roller 23 and the downstream conveyingroller 26 are driven by a conveying motor MT (see FIG. 4). The platenglass 25 has light transmissivity, and arranged below and along thesheet conveying passage 20. The conveying roller pairs 23 and 26 areconfigured to convey the original sheet GS fed by the sheet feed roller21 to pass over the platen glass 25.

According to the illustrative embodiment, the original sheets GS are tobe placed on the sheet feed tray 2 such that scan surfaces of theoriginal sheets GS face an original placement surface of the sheet feedtray 2. The scanner 24 is arranged below the sheet conveying passage 20,and is configured to scan an image on the scanned surface of eachoriginal sheet GS passes over the platen glass 25. It is noted that anoriginal sheet sensor 27 is provided to the sheet feed tray 2 such thatthe original sheet sensor 27 is turned ON when the original sheets GSare placed on the sheet feed tray 2, while turned OFF when no originalsheet GS is placed on the sheet feed tray 2.

<Details of Configuration of Scanner>

Referring to FIG. 2, a configuration of the scanner 24 will be describedin detail. The scanner 24 has a light source 30, a light receptionelement 31 and an optical member 32 as shown in FIG. 2. The light source30 includes red, green and blue light emitting diodes. Light emittedfrom the light source 30 is reflected by the scan surface of theoriginal sheet GS is directed, by the optical member 32, to the lightreception element 31. According to the illustrative embodiment, when thecolor mode is selected, one line of image on the original sheet GS isread as three-color light emitting diodes are lit sequentially. When themono mode is selected, a particular one of the three-color lightemitting diodes (e.g., the green light emitting diode) is lit to readone line of the image on the original sheet GS.

A white reference plate 34 is arranged at a position opposite to thescanner 24 with respect to the sheet conveying passage 20. That is, thewhite reference plate 34 faces the scanner 24 via the sheet conveyingpassage 20. The white reference plate 34 has a reflectance the same asthat of background color (i.e., white) of the original sheet GS. Whenthere are no original sheets GS in the sheet conveying passage 20, thelight emitted from the light source 30 is reflected by the whitereference plate 34. Then, the reflected light is received by the lightreception element 31 via the optical member 32. According to theillustrative embodiment, the optical member 32 includes a rod lensextending in a main scanning direction MD.

The light reception element 31 includes multiple sensor IC (integratedcircuit) chips which are linearly arranged in the main scanningdirection MD. Each sensor IC chip includes a plurality of photoelectricconversion elements 33 arranged in the main scanning direction MD.Further, each sensor IC chip includes a shift register and an amplifier(not shown). Each photoelectric conversion element 33 is an elementcorresponding to one pixel of image data.

<Electrical Configuration of Image Scanning Apparatus>

Referring to FIGS. 3 and 4, an electrical configuration of the imagescanning apparatus 1 will be described. As shown in FIG. 3, the imagescanning apparatus 1 has an AC/DC convertor 48, a DC/DC convertor 49, adriving circuit 47, the scanner 24 and a controller 50. Among suchcomponents, the AC/DC convertor 48 and the DC/DC convertor 49 areconvertors that convert voltages, and supply different voltages to thedriving circuit 47, the scanner 24 and the controller 50. The controller50 has a CPU (central processing unit) 40, a ROM (read only memory) 41,a RAM (random access memory) 42, a device controller 44 and an imageprocessor 46, and controls operations of the image scanning apparatus 1.Controlling of the operations by the controller 50 will be described indetail later.

The AC/DC convertor 48 converts an AC voltage of 100V into a DC voltageof 24V, and applies the converted DC voltage to the DC/DC convertor 49.According to the illustrative embodiment, the AC/DC convertor 48 employsa diode bridge and well-known circuits such as an integration circuit,and converts the AC voltage of 100V to the DC voltage of 24V.

The DC/DC convertor 49 applies a PWM (pulse width modulation) control tothe DC voltage of 24V supplied from the AC/DC circuit 48 in accordancewith a PWM setting value, and integrates the output of the AC/DC circuit48 with an integration circuit to generate a necessary DC voltage. Forexample, a DC voltage 3.3V to be applied to the scanner 24 is generatedby applying the PWM control to the DC voltage of 24V with the conductionrate of 13.75% (=3.3V/24V). A DC voltage of 1.8V to be applied to thecontroller 50, and the DC voltage of 24V for the driving circuit 47 isgenerated similarly by applying the PWM control. One interval in the PWMcontrol of the DC/DC convertor 49 is a switching cycle.

As shown in FIG. 4, the image scanning apparatus 1 has a CPU 40, a ROM41, a RAM 42, a flash PROM (programmable ROM) 43, a device controller44, an analog front end (hereinafter, abbreviated as AFE) 45, an imageprocessor 46 and a driving circuit 47 as parts of components thereof.These components are connected to the operation panel 5, the display 6and an original sheet sensor 27 via a bus 48.

The ROM 41 stores programs for executing a maintenance main process, ascanning main process, which will be described later, subroutines calledin respective main processes, and the like to control operations of theimage scanning apparatus 1. The CPU 40 controls the components of theimage scanning apparatus 1 in accordance with the programs retrievedfrom the ROM 41. The flash ROM 43 is a rewritable non-volatile memoryand stores pieces of data which are output when the CPU 40 executescontrolling of the components of the image scanning apparatus 1. Suchdata includes black data BK and white data WH which are obtained in themaintenance main process. The RAM 42 temporarily stores calculationresults generated in controlling processes of the CPU 40.

The device controller 44 is connected to the scanner 24, and transmits asignal to control turning ON/OFF of the light source 30, and a signal tocontrol an electrical current value flowing through the light source 30to the scanner 24. Further, the device controller 44 transmits a clocksignal CLK and a serial in signal SI to the light reception element 31so that the multiple photoelectric conversion elements 33 of the sensorIC chip are sequentially driven. The clock single CLK represents timingsto drive the photoelectric conversion elements 33 on pixel basis, and aline cycle signal. When the scanner 24 receives a lighting controlsignal from the device controller 44, the scanner 24 turns on the lightsource 30 and transmits an analog signal corresponding to the amount oflight received by the light reception element 31 to the AFE 45.

The AFE 45 is connected to the scanner 24, and converts the analogsignal transmitted from the scanner 24 to a digital signal at a samplingtiming for each pixel, which sampling timing is determined by a samplingvalue that is set in accordance with a command from the CPU 40. The AFE45 has a particular input range and a particular resolution which aredetermined in advance. For example, the resolution is represented bygradation value from “0” to “1023” for 10 bits. In this case, the AFE 45converts the analog signal transmitted from the scanner 24 to thedigital signal representing a 10-bit (i.e., 0-1023) digital image data.The digital image data converted by the AFE 45 is transmitted to theimage processor 46.

The image processor 46 includes an ASIC (application specific integratedcircuit) that is an IC (integrated circuit) dedicated to an imageprocessing, which applies various image processing operations to thedigital image data. The image processing operations include compensationprocesses such as a shading compensation process, and a resolutionconversion process. The image processor 46 applies the shadingcompensation process to the digital image data based on the black dataBK and the white data WH, thereby the digital image data being convertedto gradation values. Further, the image processor 46 executes theresolution conversion process by outputting the gradation values in athinned manner. The image processor 46 executes the shading compensationprocess and the resolution conversion process in accordance with settingvalues set to the image processor 46, and stores the digital image dataor the gradation values in the RAM 42. It is noted that the white dataWH and the black data BK used in the shading compensation are set to theimage processor 46.

The driving circuit 47 is connected to the conveying motor MT, anddrives the conveying motor MT in accordance with a diving commandtransmitted from the CPU 40. The driving circuit 47 rotates theconveying motor MT in accordance with a rotation amount and a rotationdirection instructed by the driving command. When the conveying motor MTrotates a particular amount, the conveying roller pairs 23 and 26 rotateby a particular angle, thereby the original sheet GS is conveyed by aparticular distance in the sheet conveying passage 20.

<Electrical Operation of Image Scanning Apparatus>

Referring to FIG. 5, an electrical operation of the image scanningapparatus 1 will be described. The DC/DC convertor 49 generates a DCvoltage of 3.3V as a voltage to be supplied to the scanner 24 inaccordance with the PWM control as mentioned above. Therefore, on the DCvoltage 3.3V, ripple voltages are superposed due to ON/OFF switching ofthe PWM control. The ripple voltage fluctuates in a voltage-increasingdirection when the PWM control is ON, while in a voltage-decreasingdirection when the PWM control is OFF. When the ripple voltage isgenerated in the DC voltage of 3.3V which is applied to the scanner 24,the change of the ripple voltages are superposed on the analog signal.Relationships between the ripple voltage and the analog signal will beexplained referring to some design examples of the switching cycle SWTand the pixel cycle PT.

Example 1 Comparative Example

FIG. 5A shows a design example 1, which is designed such that theswitching cycle SWT is 333 ns (nanoseconds) and an image pixel cycle IPTis 250 ns (nanoseconds). In the following description on FIG. 5A, thedesign example will be described referring to a first pixel to thefourth pixel of the analog signal.

In design example 1, the fluctuation amount of the ripple voltage at asampling timing of the first pixel is 60%. It is noted that thefluctuation is a value calculated based on the maximum value being 100%and the minimum value being 60%. Thus, the analog signal of the firstpixel is affected by 60% of the fluctuation amount due to the ripplevoltage.

The sampling timing of the second pixel is after the sampling timing ofthe first pixel by the pixel cycle IPT. The fluctuation of the ripplevoltage at the sampling timing of the second pixel is 92%. In the designexample 1, the pixel cycle IPT is shorter than the switching cycle SWTby approximately 25%. As a result, at the sampling timing of the secondpixel, the fluctuation of the ripple voltage is 92%. That is, thefluctuation by the 92% of the ripple voltage affects the analog signalof the second pixel.

The sampling timings for the third and fourth pixels are also after thepixel cycle IPT with respect to sampling of the previous pixel.Therefore, the fluctuation of the ripple voltage at the sampling timingfor the third pixel is 8%, and the fluctuation of the ripple voltage atthe sampling timing for the fourth pixel is 37%. As above, according tothe design example 1, influences of the fluctuation of the ripplevoltage for the multiple pixels are not constant.

Design Example 2

Referring to FIG. 5B, a case where the image scanning apparatus 1 isdesigned such that the switching cycle SWT is 250 ns, and the pixelcycle IPT is 250 ns will be described. Similarly to the case of thedesign example 1, description will be made with respect the analogsignals for the first to fourth pixels.

As mentioned above, the sampling timing for the second pixel is afterthe sampling timing for the first pixel by the pixel cycle IPT. Thefluctuation of the ripple voltage at the sampling timing for the secondpixel is 46%. According to the design example 2, the pixel cycle IPT isequal to the switching cycle SWT. Therefore, according to the designexample 2, the fluctuation of the ripple voltage for the first pixel andthat of the second pixel are constant.

The sampling timings for the third and fourth pixels are also after thesampling timing for the previous pixel by the pixel cycle IPT.Therefore, the fluctuation of the ripple voltage at the sampling timingfor the third pixel is also 46%. So is for the fourth pixel. As above,according to the design example 2, the fluctuation of the ripple voltageis constant at the sampling timing for each pixel. Therefore, theconstant fluctuation of the ripple voltage influences on the analogsignal.

Design Example 3

Referring to FIG. 5C, a case where the image scanning apparatus 1 isdesigned such that the switching cycle SWT is 125 ns, and the pixelcycle IPT is 250 ns will be described. Similarly to the cases of thedesign examples 1 and 2, description will be made with respect theanalog signals for the first to fourth pixels.

According to the design example 3, the fluctuation of the ripple voltageat the sampling timing of the first pixel is 96%. That is, the analogsignal for the first pixel is influenced by the fluctuation of theripple voltage of 96%.

As mentioned above, the sampling timing for the second pixel is afterthe sampling timing for the first pixel by the pixel cycle IPT. Thefluctuation of the ripple voltage at the sampling timing for the secondpixel is 96%. According to the design example 3, the pixel cycle IPT istwice the switching cycle SWT. Therefore, according to the designexample 3, the fluctuation of the ripple voltage for the first pixel andthat of the second pixel are constant since the pixel cycle IPT is aninteger multiple of the switching cycle SWT.

The sampling timings for the third and fourth pixels are also after thesampling timing for the previous pixel by the pixel cycle IPT.Therefore, the fluctuation of the ripple voltage at the sampling timingfor the third pixel is also 96%. So is for the fourth pixel. As above,according to the design example 3, the fluctuation of the ripple voltageis constant at the sampling timing for each pixel. Therefore, theconstant fluctuation of the ripple voltage influences on the analogsignal. It is noted that in the description of the operation of theimage scanning apparatus 1 according to the illustrative embodiment, itis assumed that the image scanning apparatus 1 is configured byemploying the design example 3.

It is noted that, if the switching cycle SWT is designed to be 125 ns,due to individual differences, the actual switching cycle SWT mayfluctuate within a range between −10% and +10%. That is, the actualswitching cycle SWT may fluctuate within a range from 112.5 ns to 137.5ns. Therefore, unless the switching cycle SWT is multiple integer of thepixel cycle PT, the fluctuation of the ripple voltage may not beconstant for respective pixels. In order to overcome this problem, asdescribed later, a line cycle determining process (R2, M2) should bedone. With this process, the fluctuation of the ripple voltage withinone line can be made constant for respective pixels within the line.

Operation According to Illustrative Embodiment

Referring to flowcharts, an operation of the image scanning apparatus 1will be described. The image scanning apparatus 1 mainly executes amaintenance main process which is executed prior to scanning of originalsheets GS and a scanning main process in which the original sheets GSarea scanned. It is noted that steps S61-S68 of the maintenance mainprocess, and steps S71-S79 of the scanning main process are executed bythe CPU 40.

<Maintenance Main Process>

The maintenance main process shown in FIG. 6 is executed before theimage scanning apparatus 1 is shipped from a factory, or when a serviceperson performs a maintenance operation of the image scanning apparatus1 after it was shipped. The maintenance main process is started when theservice person or the like operates the operation panel 5 of the imagescanning apparatus 1 according to a particular operation procedure.

The CPU 40 sets scan setting values for the device controller 44, theAFE 45 and the image processor 46 (S61). Specifically, the CPU 40obtains setting values of a clock signal CLK and a serial-in signal SIfrom the flash PROM 43, and sets the same to the device controller 44.Further, the CPU 40 obtains an offset value, a gain adjustment value anda sampling value of the AFE 45 from the flash PROM 43 and sets the sameto the AFE 45. The setting value of the clock signal CLK is a settingvalue for transmitting a signal of one pixel of the shift registerincluded in the light reception element 31. Thus, the setting value ofthe clock signal CLK is a value corresponding to an output speed for onepixel of the analog signal which is output by the light receptionelement 31. The sampling value is a value indicating a timing at whichthe analog signal is converted to the digital signal, and is set foreach pixel. According to the illustrative embodiment, the sampling cycleis set to 250 ns, and the pixel cycle is set to 250 ns. The offsetadjustment value is a value to shift a level of the analog signal inputto the AFE 45, and the gain adjustment value is a value used to adjust again of the analog signal input to the AFE 45. The CPU 40 does not makethe image processor 46 execute a shading compensation, but causes theimage processor 46 to store the digital image data in the RAM 42.

The CPU 40 determines a line cycle (S62). That is, the CPU 40 obtainsblack data BK with the light source 30 being turned off (FIG. 8: S801).Then, the CPU 40 calculates an extreme value EP of the black data BK(S802). The CPU 40 calculates ripple interval RPI based on a distancebetween extreme values (S807). Further, the CPU 40 calculates the linecycle LP such that the line cycle is an integer multiple of the rippleinterval RPI (S808). When the line cycle LP is determined (S812: NO;S823: NO), the CPU 40 sets an error flag to OFF, while when the linecycle has not been determined (S823: YES), the CPU 40 set the error flagto ON.

The CPU 40 determines whether the error flag is ON or not (S63). When itis determined that the error flag is OFF (S63: NO), the CPU 40 sets theline cycle LP which is determined in S62 and proceeds to a step of alight amount adjustment (S65). When it is determined that the error flagis ON (S63: YES), the CPU 40 proceeds to a step of an error display(S64). In S64, the CPU 40 causes the display 6 to display an errorindication. When the error indication is displayed, the maintenance mainprocess is terminated.

In S65, the CPU 40 adjusts light amount of the light source 30. That is,the CPU 40 causes the light source 30 to emit light toward the whitereference plate 34, and adjusts the light amount ST so that the analogsignal corresponding to the reflected light becomes the maximum value ofthe AFE 45. It is noted that the light amount ST is determined based ona lighting cycle and a current value of the light source 30 for oneline.

Next, the CPU 40 obtains the black data BK (S66). That is, the CPU 40turns off the light source 30 and reads the whit reference plate 34.Then, the CPU 40 obtains the digital image data for one line as theblack data BK, and stores the thus obtained black data BK in the flashPROM 43.

Next, the CPU 40 obtains the white data WH (S67). That is, the CPU 40turns on the light source 30 at the light amount ST and reads the whitreference plate 34. Then, the CPU 40 obtains the digital image data forone line as the white data WH, and stores the thus obtained white dataWH in the flash PROM 43.

Then, the CPU 40 stores the line cycle LP, which is determined in theline cycle determining process (S62), in the flash PROM 43 (S68). WhenS68 is executed, the maintenance main process is terminated.

<Scanning Main Process>

The scanning main process shown in FIG. 7 is started when the userplaces the original sheets GS for scanning on the sheet feed tray 2 andoperates a scanning start button on the operation panel 5.

When the user operates the scanning start button, the CPU 40 sets thescan setting values (S71). That is, the CPU 40 sets the scan settingvalues for the device controller 44, the AFE 45 and the image processor46. Similar to S61 of the maintenance main process, the CPU 40 obtainssetting values of a clock signal CLK and a serial-in signal SI from theflash PROM 43, and sets the same to the device controller 44. Further,the CPU 40 sets the offset adjustment value, the gain adjustment valueand the sampling values of the AFE 45. Further, the CPU 40 does not makethe image processor 46 execute a shading compensation, but causes theimage processor 46 to store the digital image data in the RAM 42.

Next, the CPU 40 determines the line cycle (S72). Similar to S62 of themaintenance main process shown in FIG. 6, the CPU 40 obtains the blackdata BK with turning off the light source 30 (S801). Then, the CPU 40calculates the extreme value EP of the black data BK (S802). Next, theCPU 40 calculates the ripple interval based on an interval of theextreme values (S807). Then, the CPU 40 calculates the line cycle LP soas to be an integer multiple of the ripple interval RPI (S808). When theline cycle is determined (S812: NO, S823: NO), the CPU 40 sets the errorflag to OFF, while when the line cycle has not be determined (S823:YES), the CPU 40 sets the error flag to ON.

In S73 of FIG. 7, the CPU 40 determines whether the error flag is set toON. When it is determined that the error flag is set to OFF (S73: NO),the CPU 40 sets the line cycle LP, which is determined in S72, andproceeds to a step of light amount adjustment (S77). When it isdetermined that the error flag is ON (S73: YES), the CPU 40 sets theline cycle LP, which is stored in S68 of the maintenance main process(FIG. 6), and proceeds to a step of light amount adjustment (S74).

In S74, the CPU 40 adjusts the light amount of the light source 30.Specifically, the CPU 40 causes the light source 30 to emit light towardthe white reference plate 34, and adjusts the light amount ST so thatthe analog signal corresponding to the reflected light becomes themaximum value of the AFE 45. It is noted that the light amount ST isdetermined based on a lighting cycle and a current value of the lightsource 30 for one line.

The CPU 40 sets the white data WH and the black data BK to the imageprocessor 46 (S75). That is, the CPU 40 sets the black data BK and thewhite data which have been stored respectively in the flash PROM 43 inS76 and S77 of the maintenance main process to the image processor 46.

In S76, the CPU 40 executes the scan process. That is, the CPU 40 causesthe image process 46 to execute shading compensation, and store thegradation values in the RAM 42. Further, the CPU 40 scans the originalsheet GS, and stores the gradation values which are obtained by theshading compensation based on the black data BK and the white data WH inthe RAM 42. After execution of S76, the scanning main process isterminated.

In S77, the CPU 40 adjusts the light amount of the light source 30.Specifically, similar to S74, the CPU 40 causes the light source 30 toemit light toward the white reference plate 34, and adjusts the lightamount ST so that the analog signal corresponding to the reflected lightbecomes the maximum value of the AFE 45. It is noted that the lightamount ST is determined based on a lighting cycle and a current value ofthe light source 30 for one line

Next, the CPU 40 obtains the black data BK (S78). That is, the CPU 40turns off the light source 30 and reads the whit reference plate 34.Then, the CPU 40 obtains the digital image data for one line as theblack data BK, and sets the thus obtained black data BK to the imageprocessor 46.

Next, the CPU 40 obtains the white data WH (S79). That is, the CPU 40turns on the light source 30 at the light amount ST and reads the whitreference plate 34. Then, the CPU 40 obtains the digital image data forone line as the white data WH, and sets the thus obtained white data WHto the image processor 46. After execution of S79, the CPU 40 proceedsto S76.

<Determination of Line Cycle>

It is noted that the line cycle determining processes in S62 of FIG. 6and S72 in FIG. 7 are the same process, and will be described referringto FIG. 8.

When the line cycle determining process (S62, S72) is started, the CPU40 obtains the black data BK (S801). That is, the CPU 40 turns off thelight source 30 and reads the white reference plate 34. Then, the CPU 40reads the same line by 32 times to obtain 32 lines of digital imagedata, and averages the obtained image data for each pixel of the line.Then, the resultant data for one line, of which each pixel isrepresented by averaged value, is obtained as the black data BK, whichis stored in the RAM 42. Since the black data BK is based on the digitalimage data to which the shading compensation has not been applied, theripple voltage superposed on the analog signal can be distinguished fromthe black data BK. Further, since the black data BK is obtained byaveraging 32 pieces of the digital image data, random noise superposedon each piece of the digital image data can be cancelled.

In S802, the CPU 40 calculates the extreme values EP. That is, the CPU40 calculates, within one line of the black data BK, the maximum valueLMx and the minimum value LMn. Then, the CPU 40 stores the maximum valueLMx and the minimum value LMn in association with pixel positionsrespectively representing positions of the pixels exhibiting the maximumand minimum values LMx and LMn in the RAM 42.

Next, the CPU 40 calculates distance LMxI between adjacent maximumvalues (S803). That is, the CPU 40 calculates a distance between each oftwo pixels exhibiting two adjacent maximum values as the maximum valueintervals LMxI, and stores the maximum value intervals LMxI in the RAM42.

Next, the CPU 40 calculates distance LMnI between adjacent minimumvalues (S804). That is, the CPU 40 calculates a distance between each oftwo pixels exhibiting two adjacent minimum values as the minimum valueintervals LMnI, and stores the maximum value intervals LMnI in the RAM42.

Next, the CPU 40 calculates an average of the maximum value intervalsLMxI (hereinafter, referred to as an averaged distance LMxIave) in S805.That is, the CPU 40 averages all the maximum value intervals LMxI toobtain the averaged distance LMxIave.

Next, the CPU 40 calculates an average of the minimum value intervalsLMnI (hereinafter, referred to as an averaged distance LMnIave) in S806.That is, the CPU 40 averages all the minimum value intervals LMnI toobtain the averaged distance LMnIave.

Next, the CPU 40 calculates the ripple interval RPI (S807). That is, theCPU 40 calculates an average value of the averaged distances LMxIave andLMnIave, and stores the thus obtained averaged value as the rippleinterval RPI in the RAM 42.

In S808, the CPU 40 calculates the line cycle LP. That is, the CPU 40calculates the line cycle LP so as to be an integer multiple of theripple interval RPI. The thus calculated line interval LP is stored inthe RAM 42.

Next, the CPU 40 sets the scan setting values (S809). That is, the CPU40 sets the scan setting values to the device controller 44 and theimage processor 46. The CPU 40 sets the serial in signal SI such thatthe cycle of the serial in signal SI is equal to the line interval LPstored in S808. Further, the CPU 40 executes a setting to cause theimage processor 46 to execute the shading compensation and store thegradation value in the RAM 42.

In S810, the CPU 40 obtains the white gradation value WHG. That is, theCPU 40 causes the light source 30 to emit light of which amount is ST,and reads the white reference plate 34 thirty-two times. Then, the CPU40 obtains the gradation values for thirty-two pieces data for one lineas the white gradation values WHG and stores the thus obtained whitegradation data WHG in the RAM 42.

Next, the CPU 40 calculates determination data DC (S811). That is, theCPU 40 calculates the determination data DC by subtracting a minimumvalue of 32 gradation values from a maximum value of 32 gradation valuesfor each pixel based on the white gradation values WHG consisting of 32pieces of gradation data for one line.

In S812, the CPU 40 determines whether the determination data DC has avalue greater than a particular vale. When the determination data DCincludes a value which is greater than the particular value (S812: YES),the CPU 40 proceeds to S814. When it is determined that thedetermination data DC includes only values equal to or less than theparticular value (S812: NO), the CPU 40 establishes the line cycle LPcalculated in S808 and proceeds to S813, at which the CPU 40 sets theerror flag to OFF. After execution of S813, the CPU 40 makes a settingto store the digital image data in the RAM 42 without making the imageprocessor 46 execute the shading compensation, and terminates the lineinterval determining process (S62, S72). According to the illustrativeembodiment, the particular value is 3% of the resolution 1024 forblack/white color. Since the particular value is 3% of the black/whiteresolution, influence of the ripple voltage on the scanned image can besuppressed.

The CPU 40 calculates a difference LMnIdif of the minimum valueintervals (hereinafter, referred to as the minimum value intervaldifference LMnIdif) in S814. Specifically, the CPU 40 obtains theminimum value interval difference LMnIdif by subtracting the minimumvalue of the minimum value intervals LMnI from the maximum value of theminimum value intervals LMnI. The CPU 40 stores the thus obtainedminimum value interval difference LMnIdif in the RAM 42.

The CPU 40 calculates a difference LMxIdif of the maximum valueintervals (hereinafter, referred to as the maximum value intervaldifference LMxIdif) in S815. Specifically, the CPU 40 obtains themaximum value interval difference LMxIdif by subtracting the minimumvalue of the maximum value intervals LMxI from the maximum value of themaximum value intervals LMxI. The CPU 40 stores the thus obtainedmaximum value interval difference LMxIdif in the RAM 42.

In S816, the CPU 40 determines whether the maximum value intervaldifference LMxIdif is greater than the minimum value interval differenceLMnIdif. When it is determined that the maximum value intervaldifference LMxIdif is greater than the minimum value interval differenceLMnIdif (S816: YES), the CPU 40 sets the averaged minimum value intervalLMnIave to the ripple interval RPI (S818).

In S817, the CPU 40 sets the average maximum value interval LMxIave tothe ripple interval RPI. That is, the CPU 40 stores the average maximumvalue interval LMxIave in the RAM 42 as the ripple interval RPI.

In S818, the CPU 40 sets the average minimum value interval LMnIave tothe ripple interval RPI. That is, the CPU 40 stores the average minimumvalue interval LMnIave in the RAM 42 as the ripple interval RPI.

It is noted that steps S819-S822 are similar to S808-S811. That is,calculation of the line cycle LP (S819), scan setting (S820), obtainingof the white gradation value WHG (S821) and calculation of thedetermination data DC (S822) are executed similarly to the line cycle LP(S808), scan setting (S809), obtaining of the white gradation value WHG(S810) and calculation of the determination data DC (S811). Afterexecution of S822, the CPU 40 proceeds to S823, where the CPU 40determines whether the determination data DC is greater than theparticular value.

In S823, the CPU 40 determines whether the determination data DC isgreater than the particular value. When there is a pixel of whichdetermination data DC is greater than the particular value (S823: YES),the CPU 40 proceeds to S824 without establishing the line cycle LP. InS824, the CPU 40 sets the error flag to ON. When there are only pixelsof which determination data DC is equal to or less than the particularvalue (S823: NO), the CPU 40 establishes the line cycle LP which iscalculated in S819, and proceeds to S825. In S825, the CPU 40 sets theerror flag to OFF. After execution of S824 or S825, the CPU 40 makessettings to store the digital image data in the RAM 42 without makingthe image processor 46 execute the shading compensation, and terminatesthe line cycle determining process (S62, S72).

Effects of Illustrative Embodiment

According to the illustrative embodiment, the image scanning apparatusis designed such that the pixel cycle IPT is the integer multiple of theswitching cycle SWT. Accordingly, at the sampling points of the analogsignal, the fluctuation of the ripple voltage is substantially constant.In other words, the fluctuation of the ripple voltage is substantiallyconstant for anyone of the pixels.

According to the illustrative embodiment, in the line cycledetermination process (S62, S72), based on the black data BK obtained inthe black data obtaining step (S801), the CPU 40 obtains the maximumvalues LMx and the minimum values LMn in the extreme value EPcalculating step (S802). Further, the CPU 40 calculates the maximumvalue intervals LMxI and the minimum value intervals LMnI (S803 andS804), then the average maximum value interval LMxIave and the averageminimum value interval LMnIave (S805 and S806). Thereafter, the CPU 40calculates an average value of the average maximum value intervalLMxIave and the average minimum value interval LMnIave as the rippleinterval RPI, and then, the CPU 40 calculates the line cycle LP so as tobe the integer multiple of the ripple interval RPI (S808). With thisconfiguration, it is possible that the fluctuation of the ripple voltageof each pixel in one line is substantially constant.

According to the illustrative embodiment, when it is determined that themaximum value interval difference LMxIdif is greater than the minimumvalue interval difference LMnIdif, the average minimum value intervalLMnIave is set to the ripple interval RPI, while the maximum valueinterval difference LMxIdif is equal to or less than the minimum valueinterval difference LMnIdif,

the average maximum value interval LMxIave is set to the ripple intervalRPI. Since the ripple interval RPI is calculated based on the maximumvalues LMx or the minimum values having less fluctuation, the rippleinterval can be set to well match a fluctuation cycle of the ripplevoltage.

According to the illustrative embodiment, the CPU 40 sets the line cycleLP which is calculated in S809 and S820, obtains the white gradationvalue WHG in S810 and S821, and calculates the determination data DCbased on the white gradation value WHG in S811 and S822. Further, inS812, S823, S813, S825 and S824, when it is determined that thedetermination data DC is greater than the particular value, the errorflag is set to ON, while when it is determined that the determinationdata DC is equal to or less than the particular value, the error flag isset to OFF. Therefore, the line cycle LP is determined precisely.

Modifications

It is noted that aspects of the disclosures should not be limited to theconfiguration of the above-described illustrative embodiment, butvarious modifications could be made without departing from the aspects.Some examples of such a modification will be described below.

(1) The image scanning apparatus 1 according to the illustrativeembodiment may be applied to an MFP (multi-function peripheral) which isprovided with a printer. The illustrative embodiment is described suchthat the power source of the scanner 24 is a DC 3.3 V power source. Thiscan be modified to another DC power source. Further, the power source ofthe scanner 24 may be configured to supply power to another circuit inaddition to the scanner 24.

(2) The illustrative embodiment is described mainly based on the imagescanning apparatus which is designed in accordance with the designexample 3. It should be noted that, in the image scanning apparatusdesigned in accordance with the design example 1, it is possible tocalculate the extreme values of the black data for each pixel within oneline, calculate intervals between pixels exhibiting the extreme valuesas extreme value intervals, calculate the ripple intervals based on thecalculated extreme value intervals, and calculate the line cycle LP suchthat the line cycle LP is an integer multiple of a value that is thecalculated ripple interval multiplied by the pixel cycle. Determiningthe line cycle LP as above, the fluctuation of the ripple voltage foreach pixel of each line.

(3) In the above-described illustrative embodiment, the line cycle LP isdetermined based on the black data BK (S62, S72), this determination maybe made based on data of intermediate color. Alternatively, the linecycle LP may be determined based on the voltage of the power source forthe scanner 24.

(4) In the above-described illustrative embodiment, the determinationdata is calculated using the white gradation value WHG in S811 or S822.This process may be modified to use gradation value of the intermediatecolor such as gray.

(5) In the above-described embodiment, the extreme values of the blackdata BK are calculated, and then the ripple interval is calculated. Thisprocess may be modified such that a fluctuation of the ripple voltagethe ripple interval is calculated

What is claimed is:
 1. An image scanning apparatus, comprising: ascanner configured to read an original sheet on a line basis at aconstant line cycle and generate analog image data for each pixel of theline, and output the analog image data for each pixel at a pixel cycle;a power source including a DC/DC convertor which is configured toconvert a first DC voltage to a second DC voltage by applying aswitching control to the first DC voltage at a switching cycle, thesecond DC voltage being supplied to the scanner; a convertor configuredto sample the analog image data at the pixel cycle to convert the analogimage data to digital image data; a sampling setting unit configured toset the pixel cycle; and a controller configured to cause the samplingsetting unit to set the pixel cycle such that the pixel cycle is aninteger multiple of the switching cycle of the DC/DC convertor.
 2. Theimage scanning apparatus according to claim 1, further comprising alight source configured to illuminate the original sheet, wherein thecontroller is further configured to: obtain black data of each pixelwithin the one line, which is output by the convertor when the lightsource is turned off; calculate extreme values for each pixel within theline based on the black data, and calculate an interval between everytwo of the pixels exhibiting the extreme values as extreme valueintervals; calculate a ripple interval based on the extreme valueintervals, the ripple interval representing an interval of a periodicalfluctuation superposed on the analog image data; and calculate the linecycle such that the line cycle is an integer multiple of the rippleinterval multiplied by the pixel cycle.
 3. The image scanning apparatusaccording to claim 2, wherein the controller further configured tocalculate maximum vales of the black data for each pixel within the oneline; calculate intervals between positions of the pixels exhibiting themaximum values as maximum value intervals; calculate minimum values ofthe black data for each pixel within the one line; and calculateintervals between positions of the pixels exhibiting the minimum valuesas minimum value intervals, wherein the controller further configuredto: calculate an average of the intervals of the maximum values as anaverage maximum value interval; calculate an average of the intervals ofthe minimum values as an average minimum value interval; and calculatean average of the average maximum value interval and the average minimumvalue interval as the ripple interval.
 4. The image scanning apparatusaccording to claim 2, wherein the controller is further configured to:calculate the maximum values of the black data for respective pixelswithin the one line; calculate the intervals between the positions ofthe pixels exhibiting the maximum values as maximum value intervals;calculate an average of the maximum value intervals as an averagemaximum value interval; and determine the average maximum value intervalas the ripple interval.
 5. The image scanning apparatus according toclaim 2, wherein the controller is further configured to: calculateminimum values of the black data for respective pixels within the oneline; calculate the intervals between the positions of the pixelsexhibiting the minimum values as minimum value intervals; calculate anaverage of the minimum value intervals as an average minimum valueinterval; and determine the average minimum value interval as the rippleinterval.
 6. The image scanning apparatus according to claim 2, whereinthe controller is further configured to: calculate maximum values of theblack data for respective pixels within the one line; calculateintervals of the positions of the pixels exhibiting the maximum valuesas the maximum value intervals; calculate minimum values of the blackdata for respective pixels within the one line; calculate intervals ofthe positions of the pixels exhibiting the minimum values as the minimumvalue intervals; calculate a maximum interval difference by subtractinga minimum value of the maximum value intervals from a maximum value ofthe maximum value intervals; calculate a minimum interval difference bysubtracting a minimum value of the minimum value intervals from amaximum value of the minimum value intervals; determines one of theaverage minimum value interval and the average maximum value intervalcorresponding to smaller one of the maximum value interval differenceand the minimum value interval difference as the ripple interval.
 7. Theimage scanning apparatus according to claim 2, further comprising: aline setting unit configured to set a line to be read by the scanner; areference plate arranged at a position facing the scanner; and acompensation unit configured to apply shading compensation to thedigital image data to output gradation values, wherein the controller isconfigured to: obtain, by multiple times, white gradation values ofrespective pixels within one line of image data output by thecompensation unit with the light source being turned on; calculatedetermination data which is a difference obtained by subtracting aminimum value of the white gradation values from a maximum value of thewhite gradation values; determine the line cycle based on thedetermination data; and set the line cycle to the line setting unit. 8.The image scanning apparatus according to claim 7, wherein thecontroller determines the line cycle when the determination datarepresents a value equal to or less than a particular value, and whereinthe controller does not determine the line cycle when the determinationdata represents a value greater than the particular value.
 9. The imagescanning apparatus according to claim 8, wherein the controller isconfigured to calculate the determination data before a pre-scan processand during the pre-scan process, and wherein, when the determinationdata obtained before the pre-scan process is greater than the particularvalue, the controller does not determine the line cycle and causes theimage scanning apparatus to make an error notification.
 10. The imagescanning apparatus according to claim 9, further comprising a storage,wherein the controller is configured to calculate the determination databefore a pre-scan process and during the pre-scan process, wherein, whenthe determination data obtained before the pre-scan process is equal toor less than the particular value, the controller establishes the linecycle and stores the established line cycle in the storage as a priorline cycle, wherein, when the determination data obtained during thepre-scan process is greater than the particular value, the controllerdoes not establish the line cycle, but sets the prior line cycle to thescanner.